Irradiation - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 87

10 kGy. 12 Yeasts and lactobacilli also display unusual resistance and are particularly
troublesome when present initially in large numbers in dried or vacuum/modified
atmosphere packaged (MAP) foods. 11,13 Fungal and, in particular, bacterial spores
are very radiation resistant and exhibit D 10 values between 1 and 10 kGy. 12,14-18 In
contrast, the majority of spoilage bacteria including Pseudomanas are not highly
radiation resistant and are easily destroyed by relatively low doses; D 10 values for
most species are usually below 1 kGy. 8,10,19 Most fungi are equally radiosensitive. 20,21
In most instances the radiosensitivity of microorganisms is inexorably linked to
the nature or complexity of the food in which treatment occurs. The pH, fat, protein,
and moisture contents or water activities of various foods have been shown repeat-
edly to either enhance or reduce radiation effects on microorganisms; natural or
added preservatives and or inhibitory compounds exert similar effects. Excellent
reviews covering this topic are available. 8,11
Briefly, some additional factors that have been reported to impact on the irradi-
ation resistance of microorganisms in foods include:

1. Nature of the target microbe (bacterium, yeast, mold, virus, parasite;

genus, species, strain; Gram positive or negative; sporeformer, vegetative
cell; size and arrangement of DNA; age or phase of growth). 11,22-25

2. Initial number of microorganisms. 12,26,27

3. Physical state of the food: frozen vs. unfrozen; liquid vs. solid. 22,25-26,28-34

4. Oxidation-reduction potential in and surrounding the food. 13,35-38

5. Applied dose. 37,38

C LASSIFICATION OF R ADIATION P ROCESSES AND S OURCES

In the food industry, three principal radiation processes, classified on the basis of
applied dosage can be used to prolong shelf life. 39

1. Radappertization: High dose, also referred to as radiation sterility. Applied

dosages of radiation are in the range of 30 to 50 kGy and are designed
to eliminate most if not all microorganisms in a food. Results are similar
to those achieved when canning low acid foods.

2. Radicidation: Medium dose, typically in the range of 1 to 10 kGy, is

applied to foods with the primary intention of eliminating all non-spore-
forming pathogens including salmonellae and listeriae. Spoilage micro-
organism levels are drastically reduced. This process can be considered
equivalent to thermal pasteurization. Parasites in meat including Trichina
spiralis in pork will also be destroyed. This does not apply to viruses.
Radicidation doses are frequently applied to frozen food products.

3. Radurization: Low dose. This process can also be considered equivalent to

heat pasteurization. It is sometimes referred to as cold pasteurization, imply-
ing that the process kills microorganisms without participation of heat. Typ-
ical doses from 0.4 to 2.5 kGy are employed during treatment of foods in
order to substantially reduce the presence of specific spoilage microorgan-
isms and or to delay ripening and senescence thereby extending its usefulness